The present invention relates to the field of synthetic chemistry, and more particularly, to novel synthetic processes useful for the preparation of oxidized phospholipids, derivatives, analogs and salts thereof.
In the art of pharmacology, modified phospholipids are known in many applications. In U.S. Pat. No. 5,985,292 compositions for trans-dermal and trans-membranal application incorporating phospholipids bearing lipid-soluble active compounds are disclosed. In U.S. Pat. Nos. 6,261,597, 6,017,513 and 4,614,796 phospholipid derivatives incorporated into liposomes and biovectors for drug delivery are disclosed. In U.S. Pat. No. 5,660,855 lipid constructs of aminomannose-derivatized cholesterol suitable for targeting smooth muscle cells or tissue, formulated in liposomes, are disclosed. These formulations are aimed at reducing restenosis in arteries, using PTCA procedures.
The use of liposomes for treating atherosclerosis has been further disclosed in the PCT patent application published as WO 95/23592. Therein are disclosed pharmaceutical compositions of unilamellar liposomes that may contain phospholipids. The liposomes disclosed in WO 95/23592 are aimed at optimizing cholesterol efflux from atherosclerotic plaque and are typically non-oxidized phospholipids.
Modified phospholipid derivatives mimicking platelet activation factor (PAF) structures are known to be pharmaceutically active, affecting such functions as vascular permeability, blood pressure and heart function inhibition. In U.S. Pat. No. 4,778,912 it is suggested that one group of such derivatives has anti-cancer activity.
In U.S. Pat. No. 4,329,302 synthetic 1-O-alkyl ether or 1-O-fatty acyl phosphoglycerides compounds which are lysolechitin derivatives usable in mediating platelet activation are disclosed. In U.S. Pat. No. 4,329,302 is disclosed that small chain acylation of lysolechitin gave rise to compounds with platelet activating behavior, as opposed to long-chain acylation, and that the 1-O-alkyl ether are biologically superior to the corresponding 1-O-fatty acyl derivatives in mimicking PAF.
The structural effect of various phospholipids on the biological activity thereof has been investigated by Tokumura et al. (Journal of Pharmacology and Experimental Therapeutics. July 1981, Vol. 219, No. 1) and in U.S. Pat. No. 4,827,011, with respect to hypertension.
In Swiss patent CH 642,665 modified phospholipid ether derivatives that may have some physiological effect are disclosed.
Davies et al. (J. Biol. Chem. 2001, 276:16015) teach the use of oxidized phospholipids as peroxisome proliferator-activated receptor agonists.
In U.S. Pat. No. 6,838,452 and in WO 04/106486 (which are incorporated by reference as if fully set forth herein), by the present assignee, the preparation of well-defined oxidized phospholipids, as well as other synthetic oxidized LDL (low density lipoprotein) components, is disclosed. The disclosed compounds are reported to be highly effective in treating atherosclerosis and related diseases, as well as autoimmune diseases and inflammatory disorders. It is further reported that the oxidized phospholipid regulate the immune response to oxidized LDL. It is further reported that generally, etherified oxidized phospholipids are superior to comparable esterified oxidized phospholipids as therapeutic agents.
Oxidation of phospholipids occurs in vivo through the action of free radicals and enzymatic reactions abundant in atheromatous plaque. In vitro, preparation of oxidized phospholipids usually involves simple chemical oxidation of a native LDL or LDL phospholipid component. Investigators studying the role of oxidized LDL have employed, for example, ferrous ions and ascorbic acid (Itabe, H., et al., J. Biol. Chem. 1996; 271:33208-217) and copper sulfate (George, J. et al., Atherosclerosis. 1998; 138:147-152; Ameli, S. et al., Arteriosclerosis Thromb Vasc Biol 1996; 16:1074-79) to produce oxidized, or mildly oxidized phospholipid molecules similar to those associated with plaque components. Similarly prepared molecules have been shown to be identical to auto-antigens associated with atherogenesis (Watson A. D. et al., J. Biol. Chem. 1997; 272:13597-607) and able to induce protective anti-atherogenic immune tolerance (U.S. patent application Ser. No. 09/806,400 to Shoenfeld et al., filed Sep. 30, 1999) in mice. Similarly, in U.S. Pat. No. 5,561,052, a method of producing oxidized lipids and phospholipids using copper sulfate and superoxide dismutase to produce oxidized arachidonic or linoleic acids and oxidized LDL for diagnostic use is disclosed.
The oxidation techniques described above for preparing oxidized phospholipids involve reactions that are non-specific and yield a mixture of oxidized products. The non-specificity of the reactions reduces yield, requires a further separation step and raises concern for undesired side effects when the products are integrated in pharmaceutical compositions.
1-Palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC) and derivatives thereof such as 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) are representative examples of mildly oxidized esterified phospholipids that have been studied with respect to atherogenesis (see, for example, Boullier et al., J. Biol. Chem. 2000, 275:9163; Subbanagounder et al., Circulation Research, 1999, pp. 311). The effect of different structural analogs that belong to this class of oxidized phospholipids has also been studied (see, for example, Subbanagounder et al., Arterioscler. Thromb. Nasc. Biol. 2000, pp. 2248; Leitinger et al., Proc. Nat. Ac. Sci. 1999, 96:12010).
POVPC is typically prepared by providing a phosphatidyl choline bearing an unsaturated fatty acid and oxidizing the unsaturated bond of the fatty acid by, e.g., ozonolysis (oxidative cleavage) or using a periodate as an oxidizing agent. Such a synthetic pathway typically involves a multi-step synthesis and requires separation of most of the formed intermediates by means of column chromatography.
As described in U.S. Pat. No. 6,838,452 cited above, etherified oxidized phospholipids have been similarly prepared by oxidizing an unsaturated bond of a fatty acid attached to a phospholipid backbone. More particularly, the etherified oxidized phospholipids were prepared, according to the teachings of this patent, by introducing an unsaturated short fatty acid to a glycerolipid, introducing a phosphate moiety to the obtained intermediate and oxidizing the unsaturated bond in the fatty acid chain by means of (i) hydrogen peroxide and formic acid, so as to obtain a diol, followed by potassium periodate, so as to obtain an aldehyde; or (ii) ozonolysis. While the oxidative cleavage of the unsaturated bond results in an aldehyde moiety, other oxidized moieties (e.g., carboxylic acid, acetal, etc.) were obtained by further oxidizing the aldehyde moiety. Such a multi-step synthetic pathway is oftentimes characterized by relatively low overall yields and again, requires separation of most of the formed intermediates by means of column chromatography.
It has been found that in vivo applications employing esterified oxidized phospholipids prepared as above have the disadvantage of susceptibility to recognition, binding and metabolism of the active component in the body, making dosage and stability after administration an important consideration. Etherified oxidized phospholipids, such as those described in U.S. Pat. No. 6,838,452 and in WO 04/106486, exhibit higher biostability and high therapeutic activity.
Thus, the currently known methods of preparing etherified, as well as esterified, oxidized phospholipids involve complex multi-step procedures suitable for laboratory preparation yet rendering industrial scale preparation inefficient and complex. In particular, these multi-step procedures require industrially inapplicable separation techniques such as column chromatography during various stages of the synthetic process.
In view of the beneficial therapeutic activity of oxidized phospholipids in general and of etherified oxidized phospholipids in particular, there is a widely recognized need for and it would be highly advantageous to have an improved process for the preparation of etherified oxidized phospholipids devoid of at least some of the disadvantages of processes known in the art.